<?
  if ($_GET['logout']==1) {
    unset($_SESSION['valid_login']);
  }
?>
<table width="100%">
<tr>
<td class="style3">
	<a href="frontpage.php">Home</a>><a href="show_depart.php">Departments</a>
</td>
<td class="style3" align="right">
	<a href="<?echo $_SERVER['PHP_SELF'];?>?logout=1">Sign out</a>
</td>
</tr>
</table>